Biconical electromagnetic horn antenna



Dec. 5, 1950 G. A. JARVIS 2,53

BICONICAL ELECTROMAGNETIC HORN ANTENNA Filed Feb. 19, 1945 2 Sheets-Sheet l IPVIS INVENTOR. 36 GEORGE A. JARVIS ATTORNEY Dec. 5, 1950 G. A. JARVIS 2,532,551

BICONICAL ELECTROMAGNETIC HORN ANTENNA Filed Feb. 19, 1945 2 Sheets-Sheet 2 FIG. 2.

FIG. 3.

III I I i FIG. 4. 34 33 32 GEORGEIINIIZFIYJTQIIS ATTORNEY Patented Dec. 5, 1950 BICONICAL ELECTROMAGNETIC HORN ANTENNA George A. Jarvis, Cambridge, Mass.,'assign'or;-by mesne assignments, to the United States of America as represented liy the Secretary :of

War

Application February 19, 1945, Serial No. 578,764

2 Claims.

The present invention relates generally to ultra-high-frequency antenna structures and more particularly to suchs'tructures of the biconical electromagnetic horn type adaptedJfor use in connection with radar beacon stations.

In the horn radiator for ultra-high-frequencies, directivity isobtained by using a horn to guide and concentrate the radiated wave into a sharply defined pattern. Such radiators are capable of giving highly directional patterns when the mouth thereof has a dimension that is large relative to the wavelength. Horns become practical at ultra-high frequencies since thena dimension that is large compared with the wavelength does not entail excessive physical size. The field pattern obtained by exciting a horn radiator is determined by the shape and dimensions of the mouth measured in wavelengths'and the variation in magnitude and phase of the field distribution produced across the mouth of the horn.

When a horn radiator is employed as a receiving antenna, the mouth gathers in a section of the passing wave. If this wave is travelling..directly toward the mouth of the horn, then the horn in effect cuts out a slice of the wave having a cross section approximating that of the horn mouth. If the incoming wave approaches from an angle the effective cross section of mouth that this wave sees as it approaches the horn is reduced and the amount of energy that can be abstracted from the wave is likewise less. The end result is a directional pattern that is exactly the same as that obtained when the horn is used for transmitting.

Ingadar beacon stations, wherein an automatic transmitter is operated by a radar signal transmitted by an aircraft to enable the aircraft to determine its azimuth and range with respect to the beacon, the antenna structure associated with the beacon is required to produce a radiation pattern which is uniform in all horizontal directions and which concentrates the energy outwardly permitting a minimum amount to be scattered into the ground and a small amount to be scattered vertically upwards since aircraft positioned vertically upwards will be at relatively short ranges and hence require less signal. The desired pattern should be fairly wide vertically,

however, to obtain the desired coverage of the.

surrounding space.

The horn antenna most suited for beacon applications is that of the biconical type, consisting of a pair of conical conducting surfaces with common axis and oppositely disposed'with" nape sections adjacent. When excited in a fundamentalmode such a horn is characterized by a pancake type of radiation pattern in which the radiationis concentrated in a sharp beam in the vertical plane butis uniformly distributed in the horizontal plane.

Since a radar beacon must cover a large band width to accommodate all aircraft radar which might interrogate it, it is generally advantageous to have separate receiving and transmitting antennas. This is necessary in that a suitable duplexing device permitting the use of but a single antenna for. transmitting and receiving is extremely difficult to realize in view of its limited band width, especially at microwaves.

Accordingly, it is the principal object of this invention to provide an antenna assembly for a beacon station comprising two sets of biconical antennas for transmitting and receiving.

Another obj ect-of this invention is to provide an assembly 'ofthe above-described type which is rigidly constructed and weatherproof.

Yet another object of this invention is to provide an antenna assembly of the above-described type incorporating radiators producing a pattern having horizontal polarization.

An additional object of this invention is to provide an antenna assembly of the abovedescribed type incorporating radiators producing a'pattern having "vertical polarization.

For a further understanding of this invention, as well as other objects and features thereof, reference is made tothe following description to be read'in connection with the accompanying drawings wherein:

Figure 1 shows invertical section a preferred embodiment of a biconical antenna assembly in accordance with the invention,

Figure 2 is an enlarged view of one ofthe radiating elements and-the surrounding structure shown in Figure 1,

Figure 3- isa plan view of the radiating element'shown in Figure 2 and,

Figure 4 illustrates a radiator adapted for vertical polarization. I

Referring now to the drawings and more particularly to Figure 1, there is shown an antennaassembly comprising a biconical transmitting-antenna l0 and -a biconical receiving antenna ll.

Two sets of oppositely disposed conical reflecting surfaces are provided, the surfaces being indicated by numerals i2, I3, Hi and i5. The uppermost cone' [5 and the' lowermost cone [2 are axially apertured complementary to bushings 29. These conical surfaces are mounted concentric with the vertical axis 16 and the remainder of the antenna assembly is symmetrical with respect to this axis. The lower pair of conical surfaces, [2 and it, constitute a biconical horn which serves to concentrate to a certain degree the radiation from a radiating element ll in a vertical plane and compels the radiation pattern to be horizontally symmetrical. Radiator ll is connected through a coaxial transmission line l8 to the transmitter of the beacon.

The upper pair of conical surfaces Hi and I constitute a receiving horn having a directional pattern identical to that oi the transmitting horn. The receiving antenna i9 is connected by means of a coaxial line 2i} to the beacon receiver.

The entire assembly is vertically raised above ground and supported by means of an elevation pipe 2! concentric with coaxial line it. Lateral movement of pipe 29 is prevented by means of ring clamps 35 connected to struts (not shown). A suitable covering sleeve 22, preferably composed of Plexiglas, completely envelops the assembly to provide weatherproofingtherefor. The upper end of covering sleeve 22 is capped by a dome cover 23 which may be a cone similar to those used in the directive elements 52 and H5.

The rims or bases of reflecting surfaces E2 to [5 are flanged and bolted to the inner surface of sleeve 22. The construction details of the radiator It, as well as the supporting structure connecting reflecting surfaces iii and :3, may be more clearly viewed by referring to Figures 2 and 3. The construction details of receiving antenna 2d and the surrounding structure, being substantially identical with that of radiator ll, need not be shown.

To mount the conical surfaces rigidly and to maintain a fixed spacing therebetween, a collar 24 composed of non-conductive material is disposed between the napes of reflecting surfaces l2 and iii. The cones l2 and iii, the collar 24 and the discs 2'5 and 28 are provided with six circumferentially arranged, equally spaced, aligned bores to receive clamping bolts 25. Separating the transmitting antenna it from receiving antenna H is a separation pipe 26 bonded to an annular metal disc 27 bolted to the upper end of collar 26. The supporting pipe isbonded to a similar disc 28 bolted to the lower end of collar 2s and the coaxial line I3 is maintained coaxially within pipe 2i by means of a metal bushing 29 secured to disc 23, the said bushing being fixed through the axial aperture in the cone I2.

Radiator l 1 comprises three dipole radiating elements, each dipole having two circular segments, said segments being circumferentially arranged. The radiator is mounted equidistant from cones l2 and is and along axis iii. The dipoles are fed in a manner such that the current flows in the same angular direction in all elements. As is shown in Figure 8, in order to obtain the best condition of radiation impedance the bolts 25 are oriented with respect to the triple dipole radiation element H at evenly spaced positions.

Figure 4 illustrates means for constructing a unit of an antenna assembly producing a radiation pattern having vertical polarization. A biconical horn antenna is provided having two reflecting cones 30 and 3! identical in all respects with that shown in Figure 1. The radiating element herein is a section of a coaxial transmission line 32 whose outer conductor 33 is cut away over a short length thereby exposing the central conductor 34. To match the radiation impedance of this element to the transmission line, a shorting plunger 35 is employed slidably received within the coaxial line which may be adjusted in position to permit a maximum of radiated energy. In this case a bolting arrangement as shown in Figures 2 and 3 is no longer feasible since it would materially affect the radiation pattern produced, the bolts being aligned in the polarization direction.

In Figure 1 the radiator I7 and receiving antenna l9 provide radiation patterns having horizontal polarization. The coaxial line 28 leading to the receiver may extend around and down parallel to the axis of the beacon antenna Without destroying the radiation pattern. If the pattern is to be of, vertical polarization as shown in Figure 4, the coaxial line connecting the receiving antenna may be concentric with the coaxial line connecting the transmitting antenna so that they may both extend along the axis it of the unit and form a coaxial line within a coaxial line. This arrangement being obvious is not shown. The spacing of the conical surfaces in a set is kept small so that the wave front of radiation' does not produce destructive interference, in accordance with the principles underlying electromagnetic horn design.

While there have been described what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

An assembly for a pair of biconical antennae comprising two sets of truncated, conical, reflecting surfaces oppositely disposed along a common axis, the said surfaces being flanged about their bases and provided with a plurality of circumferentially arranged, equally spaced, longitudinal bores about their truncated surfaces, the uppermost and. the lowermost of said conical surfaces being axially apertured;. a nonconductive spacing collar positioned between each set of conical surfaces along the axis thereof and provided with a plurality of equally spaced longitudinal bores; a circular, metallic, recessed disc positioned against the inner truncated surface of each of said conical surfaces and about the common axis thereof, the said discs being provided with a plurality of equall spaced bores, the bores in said surfaces, collars and discs being aligned to permit passage therethrough of conductive clamping bolts, the uppermost and the lowermost of said discs being axially apertured complementar to the apertured area of the conical surface adjacent thereto; an annular, metallic bushing having a downwardly extending axial portion adapted to be inserted through the apertured areas of said conical surfaces and discs, the said apertured conical surfaces and discs and the said bushings constituting extreme upper and lower antenna elements of said assembly; radiating elements positioned equidistant between each pair of reflecting surfaces, a pair of transmission lines fixed through the said bushings and connecting one of said radiating elements to a transmitter and the other of said radiating elements to a receiver; a rigid supporting member connected between the two antennae and fixed in the intermediate recessed discs; a hollow second rigid supporting member coaxial with the lower of said transmission lines and fixed in the lower of said recessed discs; a waterproofing sleeve positioned about said antennae and fixed to the flanged bases of said conical surfaces; and a conical waterproofing cover having a downwardly extending flange and fixed about the upper portion of said sleeve, the said cap being centrally a'pertured to allow passage therethrough of the upper of said transmission lines.

2. An assembly for a pair of biconical antennae comprising two sets of truncated, conical, refleeting surfaces oppositely disposed along a common axis, the said surfaces being flanged about their bases and provided with a plurality of circumferentially arranged, equally spaced, longitudinal bores about their truncated surfaces, the uppermost and the lowermost of said conical surfaces being axially apertured; a nonconductive spacing collar positioned between each set of conical surfaces along the axis thereof and provided with a pluralit of equally spaced 1ongitudinal bores; a circular, metallic, recessed disc positioned against the inner truncated sur face of each of said conical surfaces and about the common axis thereof, the said discs being provided with a plurality of equally spaced bores, the bores in said surfaces, collars and discs being aligned to permit passage therethrough of conductive clamping bolts, the uppermost and the lowermost of said discs being axially apertured complementary to the apertured area of the conical surface adjacent thereto; an annular, metallic bushing having a downwardly extending axial portion adapted to be inserted through the apertured areas of said conical surfaces and discs, the said apertured conical surfaces and discs and the said bushings constituting extreme upper and lower antenna elements of said assembly; a pair of coaxial transmission lines fixed through said bushings, one of said transmission lines being connected to a transmitter and the other of said lines being connected to a receiver; a pair of three-element dipole radiators, each dipole having two circular elements circumferentially arranged, the said radiators terminating the said transmission lines and positioned equidistant between each pair of conical surfaces; a rigid supporting member connected between the two antennae and fixed in the intermediate recessed discs; a hollow second rigid supporting member coaxial with the lower of said transmission lines and fixed in the lower of said recessed discs; a waterproofing sleeve positioned about said antennae and fixed to the flanged bases of said conical surfaces; and a conical waterproofing cover having a downwardlyextending flang and fixed about the upper portion of said sleeve, the said cap being centrally apertured to allow passage therethrough of the upper of said transmission lines.

GEORGE A. JARVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,175,252 Carter Oct, 10, 1939 2,231,602 Southworth Feb. 11, 1941 2,368,663 Kandoian Feb. 6, 1945 2,369,808 Southworth Feb. 20, 1945 2,416,698 King Mar. 4, 1947 FOREIGN PATENTS Number Country Date 548,193 Great Britain Sept. 30, 1942 114,368 Australia Dec. 24, 1941 OTHER REFERENCES Biconical Electromagnetic Horns, by Barrow et al., published in Proceedings of the IRE, vol. 27, No. 12, December 1939, page 779. 

